This invention relates to a thermal printer/plotter provided with a parallel thermal printhead comprising a plurality of aligned thermal resistive elements for producing characters and/or graphs by means of dots on a sheet of heat-sensitive paper.
A typical parallel thermal printhead used in facsimile systems etc. is about 216 millimeter long and has 1000 to 4000 thermal resistive elements with a density of 6 to 16 elements per millimeter. These elements are usually divided into several groups each consisting of several hundred elements so that the elements are energized sequentially one group after another. In particular, for printing a whole line the elements of all the groups are energized group by group, and the period of time of energization is in the order of 1 ms per group. On the other hand, the amount of electric power required for energization of one resistive element is about 0.1 to 1 W, so that the total amount of power required for simultaneous energization of all the elements in one group containing several hundred elements exceeds 100 W. Usually the power required for energization of a thermal printhead is supplied by a DC source of 12 to 24 V. If a power of 120 W is to be supplied at DC 12 V, a current of 10 A is required. This means that a power source having a current capacity of more than 10 A is required.
As described above, in order to drive a thermal printhead having one to several thousand thermal resistive elements a DC power source with a current capacity of more than 10 A is required. A power source having such a high current capacity is large in size and expensive in cost.